In recent years, two major developments have been affecting telecommunications technology: broadband communication and mobile communication.
Broadband communication is mainly driven by new multimedia services which require more bandwidth than can be offered by existing network solutions.
ATM (Asynchronous Transfer Mode) is considered the major technology for future development of Broadband Integrated Services Digital Networks (B-ISDN). Standards supported by the International Telecommunications Union as well as the ATM Forum are evolving to allow seamless interworking of equipment and networks which are manufactured and operated by different organizations. The intent behind using ATM is also to create a single network that is able to handle different kinds of telecommunications traffic, including video, data and audio.
An ATM transport network (i.e., a communication network which transmits information using ATM cell packets) is known to include an ATM layer and a physical layer. The ATM layer is based on the virtual path/virtual channel (VP/VC) concept. The VC identifies a unidirectional communication capability through which ATM cells are transported. One or more VCs can be used in a particular virtual path (VP), which also (in general) identifies another level of the communication capability through which the ATM cells are transported.
An ATM cell (as the smallest information unit) includes a header field (5 bytes or octets) and a payload field (48 bytes or octets). The ATM cell header contains the VP and VC identifier(s) used for addressing inside the network (i.e., for routing the information to an intended destination).
Communication in known ATM networks is initiated during a connection setup, after which cells belonging to one connection follow a predetermined path defined by the VPI and VCI on a particular link. The connection control information transferred during setup utilizes a unique Signalling VC (SVC) which is contained in the VP used. It is identified by the pair: virtual path ID (VPI) and virtual channel ID (VCI). The physical layer provides a reliable continuous physical (hardwired) connection between ports of the user side and of the network side.
Mobile communication via wireless interface has gained significant importance for voice and data transmission. Cellular architecture, with its limited coverage areas for each radio cell, allows frequency reuse and therefore accommodates a large number of mobile users. These radio cells can be located statically based on fixed access points using ground-mounted stations or geostationary satellites. The radio cells can also be located dynamically using non-fixed access points such as low earth orbit satellites, for example. To allow mobility of the mobile terminals across the borders of adjacent radio cells, systems typically provide special mechanisms for handover, new registration, and connection-loss.
FIG. 2 illustrates the structure of a known cellular wireless network having a controller 10, a plurality of access points 12, and a mobile terminal 14. Controller 10 can be implemented in a central device, or its functions may be distributed among the access points 12. As the mobile terminals move across the radio cell boundaries 16, ongoing communications continue without impacting the telecommunications connection. Mechanisms for registration of a new mobile terminal, handover of an existing mobile terminal, and loss of connection with a mobile terminal, are all provided. However, the wireless communication connection between the mobile terminal 14 and the controller 10 must be processed (i.e. translated) at the access points 12. The controller must rely on the access points to perform the necessary translations for information passing to/from the mobile terminals. Therefore, the access points require complex processing hardware and software. The result is a costly access point, both in terms of cost and processing time.
In wireless networks, it is known to use electromagnetic (radio or optical) links between mobile terminals (MT) and the network. These electromagnetic links are less reliable than fixed (hardwired) network links. The area of the wireless network is typically split into radio cells, shown in FIG. 2, in order to increase the total capacity of the network and the reduce transmission power. Adjacent radio cells use different frequency domains. Each radio cell is controlled by an access point which typically includes a radio controller responsible for monitoring the electromagnetic transmissions in its access point's frequency domain. One or more access points are controlled by the system controller.
Current telephone networks use synchronous transfer modes in which timeslots are specifically reserved in constant intervals, i.e. transmitter and receiver are synchronized to detect the selected timeslot.
Due to the limited bandwidth in current wireless systems, e.g., GSM, the ability of known systems to handle future bandwidth intensive services is limited as well. Network proposals which offer higher bandwidth lack the interoperability with the future B-ISDN.
The present invention therefore desires to combine both technological directions: ATM and wireless networking. The major hurdle for an integrated solution is that ATM is designed primarily for wired networks. Adaptation of the virtual channel/virtual path (VC/VP) concept, which is inherent in ATM, to the wireless environment is one of the major problems that the present invention attempts to solve.
Accordingly, it is one object of the present invention to provide a system which has an inexpensive and reliable infrastructure with simplified access points (AP).